Distillation is a major factor in the capital and operating costs for the petroleum refining, synthetic fuel, petrochemical, and chemical industries. Most distillation operations are conducted in tray towers in which the liquid flows across the trays and down the column by way of downcomers, while the gas passes upward through the trays. Mass transfer occurs in the liquid-gas mixtures near the bottom of each tray. Phase separation, necessary to secure overall countercurrent flow of gas and liquid, occurs by gravity because of the spaces between the trays. Reduction in the size and cost of distillation columns would be of major benefits to the industries mentioned above, but such reductions are difficult if not impossible to achieve with respect to the distillation column equipment presently and heretofore known. Because of the principals according to which conventional distillation equipment operates, relatively large vertical separation between adjacent trays is necessary to achieve adequate phase separation. Reduction of horizontal dimensions of distillation columns is not practical because reductions of the spaces between the elements employed would result in diminishment of the distillation column capabilities. This invention seeks to provide methods and apparatus for distillation and related processes in which the apparatus is of substantially reduced size and cost, yet which efficiently accomplishes adequate separations by the processes.